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PCT

WORLD INTELLECTUAL PROPERTY ORGANIZATION
International Bureau

INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)

(51) International Patent Classification 5 :
G01N 27/26

(11) International Publication Number: WO 94/25705

(43) International Publication Date: 22 December 1994 (22.12.94)

(21) International Application Number: PCT/US94/05322

(22) International Filing Date: 13 May 1994 (13.05.94)

(30) Priority Data:
08/073,178

8 June 1993 (08.06.93)

(71) Applicant: BOEHRINGER MANNHEIM CORPORATION

[US/US]; 9115 Hague Road, Indianapolis, IN 46250 (US).

(72) Inventors: WHITE, Bradley, E4 3712 Langston Drive, Indi-

anapolis, IN 46268 (US). PARKS, Robert, A; 1447 E. Co.
Road, 750 N, Springport, IN 47386 (US). RITCHIE, Paul,
G.; 7617 Iron Horse Lane, Indianapolis, IN 46256 (US).

(74) Agents: GREEN, Clarence, A. et al; Perman & Green, 425
Post Road, Fairfield, CT 06430 (US).

(81) Designated States AU, CA, JP, KR, NZ, European patent (AT,
BE, CH, DE, DK, ES, FR, GB, GR, IE, IT, LU, MC, NL,
PT.SE).

Published

With international search report.
With amended claims.

(54)ThIe: ^SENSING METER WHICH DETECTS PROPER ELECTRODE ENGAGEMENT AND DISTINGUISHES SAMPLE AND
CHECK STRIPS

(57) Abstract

A biosensing meter (50) receives a biomedical
sample strip (10) which includes electrically isolated
excitation (14) and sense (12) electrodes or, alternatively,
a check strip. The biosensing meter includes first and
second contacts (C, D) mat are connected by a sense
electrode upon insertion of a sample strip. An operational
amplifier circuit has first and second inputs respectively
connected to the first contact and a reference potential, the
first input manifesting the reference potential as a result of
a feedback within the operational amplifier. A processor
(60) is coupled to the second contact and determines
the presence of the reference potential at the second
contact when an inserted sense electrode connects the first
and second contacts. The processor also distinguishes
between sample and check strips and tests for a proper
impedance between the sense and excitation electrodes of
a sample strip, thus enabling operation of the biosensing
meter upon sample strip dosing.

FOR THE PURPOSES OF INFORMATION ONLY

Codes usee

1 toidentif

f States party to the PCT oo the front pages of pamphlets publishing international

apphcahons. under

the PCT. '

Austria

United Kingdom

Australia

Georgia

Malawi

BB
BE

Barbados

Guinea .

Niger

Netherlands

Belgium

Greece

Burkina Fiso

Hungary

Norway

Bulgaria

Ireland

New Zealand

Benin

Italy

Poland

Brazil

Japan

Portugal
Romania

Belarus

Kenya

Canada

Kyrgystan

Russian Federation

Central Africa

n RepnbBo

Democratic People's RepubBc

Sudan

Congo ..

of Korea

Sweden

. Switzerland

KB.

Republic of Korea

Slovenia

Cote dTIvoire

v Kazakhstan

Slovakia

. Cameroon

Senegal

China

Sri Lanka

Chad

Luxembourg

Togo

Czech Repubi

Latvia

Tajikistan

Gcnnany

Monaco

Trinidad and Tobago

Denmark

Republic of Moldova

Ukraine

Spam

Madagascar

United States of America

Mafi

Uzbekistan

Ranee

Mongolia

Viet Nam

Gabon

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BIOSENSING METER WHICH DETECTS PROPER ELECTRODE ENGAGEMENT
AND DISTINGUISHES SAMPLE AND CHECK STRIPS

5 FIELD OF THE INVENTION

This invention relates to biosensing instruments for
detecting analyte concentrations and, more particularly, to
such instruments that employ disposable sample strips.

BACKGROUND OF THE INVENTION

Biosensing instruments that employ disposable sample strips
enjoy wide consumer acceptance. Such instruments are

15 employed for the detection of analytes such as glucose and
cholesterol levels in blood samples and, in general,
provide accurate readings if the user is careful to follow
the instrument's directions. More often than not, however,
the user is careless in the use of either the sample strip

20 or the instrument and erroneous readings result.
Accordingly, significant efforts have been taken by
instrument manufacturers to reduce the potential for errors
during the use of sample strips and instruments.

25 Even if a biosensing instrument and sample strips are
employed properly, the presence of a manufacturing defect
in either will cause erroneous readings. Thus, while great
care is taken in the production of such instruments and
sample strips, there is a need to incorporate analytical

30 procedures in the instrument that enable instrument
malfunctions, sample strip irregularities, and user errors
to be detected so as to prevent erroneous analyte readings.

The prior art includes a number of disclosures of
35 biosensing instruments that employ disposable sample
strips. In U.S. Patent 5,108,564 to Szuminsky et al., a
biosensing instrument is disclosed that measures glucose
concentrations in blood. The instrument depends upon a
reaction wherein glucose, in the presence of an enzyme,

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catalyzes a reaction of potassium ferricyanide to potassium
ferrocyanide. After the reaction has completed, a voltage
is applied across a reaction zone and causes a reversal of
the reaction with an accompanying generation of a small,
5 but measurable current. That current is termed the
Cottrell current and, in dependence upon the concentration
of glucose in the reaction zone, follows a predetermined
curve during the reverse reaction. A reading of the
Cottrell current is converted into an indication of glucose

10 concentration. The instrument senses an impedance across
the reaction zone and determines when a blood sample has
been emplaced therein by detecting a sudden change in
current flow. At such time, an incubation period is
commenced, followed by application of a potential across

15 the reaction zone and measurement of the Cottrell current.

European Patent Application 0 471 986 A2 of Tsutsumi et al.
discloses a blood glucose measurement system that employs
disposable sample strips. The Tsutsumi et al. system

20 detects the presence of a blood sample by sensing a
resistance across a pair of electrodes. It further employs
a plurality of sensor-like strips, each having a specific
resistance value which identifies it from other strips.
Each of these strips has a particular application, i.e.,

25 for use during an adjustment mode of the instrument, during
an error compensation mode, during a calibration mode, etc.

U.S. Patent 4,999,582 to Parks et al., assigned to the same
Assignee as this application, describes a biosensor

30 electrode excitation circuit for determining if a sample
strip has been properly inserted into a meter and if at
least one electrode on the sample strip exhibits a proper
level of contact resistance. U.S. Patent 4,123,701 to
Josef sen et al. also describes a dual electrode sample

35 strip which employs a recessed well for receiving a
biological sample. The instrument which receives the
sample strip is provided with an opening that accommodates
the sample strip and prevents its insertion in an erroneous

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manner. In U.S. Patent 3,922,598 to Steuer et al., an
electrical resistance system is described for measuring
hematocrit of a blood sample. In this instance, however,
an electrode probe is employed for measuring the required
5 resistance value - rather than a disposable sample strip.

U.S. Patent 4,940,945 to Littlejohn et al. describes an
interface circuit for use in a biochemical sensing
instrument. A disposable cartridge is employed that

10 includes a pair of electrodes across which resistance
measurements are taken* Circuitry is disclosed for sensing
the presence of a fluid sample by an initial resistance
measurement. In Fig. 10, Littlejohn et al. indicate that
electrical contact is made to an electrode by a pair of

15 measurement contacts so that a current flows that is
sufficiently high to create a microweld-f or purposes of
improved electrical contact. U.S. Patent 3,996,514 to
Brown et al. employs plural electrodes to enable contact
resistance to be measured and monitored during use of a

20 circuit board.

Accordingly, it is an object of this invention to provide
a biosensing meter with an ability to determine whether a
sample strip has been properly or improperly inserted.

It is another object of this invention to provide a
biosensing meter with the capability for discriminating
between a sample strip and a check strip.

30 It is another object of this invention to provide a
biosensing meter that accepts reusable sample strips and
determines the quality of the sample strip upon its
insertion.

35 SUMMARY OF THE INVENTION

A biosensing meter receives a biomedical sample strip or a
check strip, a sample strip including electrically isolated

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excitation and sense electrodes* The biosensing meter
includes first and second contacts that are positioned to
be electrically connected by a sense electrode when a
sample strip is inserted into the biosensing meter. An
5 operational amplifier circuit has one input connected to
the first contact and a second input connected to a
reference potential, the one input manifesting the
reference potential as a result of a feedback within the
operational amplifier. A processor is coupled to the

10 second contact and determines the presence of the reference
potential at the second contact when an inserted sense
electrode connects the first and second contacts. The
processor also distinguishes between a sample strip and a
check strip and, when a sample strip is inserted, that the

15 sample strip exhibits a proper impedance between its sense
and excitation electrodes - to enable operation of the
biosensing meter upon dosing of the sample strip.

DESCRIPTION OP THE DRAWINGS
Fig. 1 is a plan view of a sample strip.

Fig. 2 is a plan view of a check strip with a top cover
removed.

Fig. 3 is a circuit/block diagram of a biosensing meter
that embodies the invention.

Fig. 4 shows a circuit arrangement when a check strip is
30 inserted into the biosensing meter of Fig. 3.

Fig. 5 is a diagram illustrating levels of sensed currents
that enable strip type discriminations to be made and a
determination of the quality of an inserted strip.

Fig. 6 is a flow diagram illustrating the operation of the
circuit of Fig. 3.

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DETAILED DESCRIPTION OF THE INVENTION

Referring to Fig. 1, sample strip 10 coraprisies a pair of
electrodes 12 and 14 which are supported on a polymeric
5 support 16. A cover sheet 18 is provided with openings 20
and 24 which expose electrodes 12 and 14 . Opening 20
creates a well and defines a reaction zone between
electrodes 12 and 14. A layer (not shown) of enzymatic
reactants overlays electrodes 12 and 14 and provides a
10 substrate on which an analyte - containing fluid sample can
be emplaced. Opening 24 exposes electrodes 12 and 14 so
that when sample strip 10 is inserted into a biosensing
meter, electrical connection can be made thereto,

15 In Fig. 2, a check strip 30 is shown that is employed to
determine the operability of the biosensing meter and to
enable an exercise of certaiin of its measurement functions.
Check strip 30 includes a pair of electrodes 32 and 34
which correspond in placement to sense and excitation

20 electrodes 12 and 14 (Fig. 1) respectively. Electrode 32
is foreshortened and is bounded by an L-shaped electrode 36
that is shorted by wire 38 to electrode 34. A resistance
40 connects electrodes 32 and 36 to electrode 32. As will
be hereafter understood, check strip 30 enables an exercise

25 of a biosensing meter's measurement functions.

In Fig. 3, a schematically illustrated biosensing meter 50
includes a window (not shown) for accepting either a sample
strip 10 or a check strip 30. In Fig. 3, the distal

30 portion of .a sample strip 10 is shown in the inserted
position. Excitation electrode 14, if it is continuous and
properly inserted, electrically connects contacts A and B.
Similarly, sense electrode 12 electrically shorts contacts
# c and D if sample strip 10 is properly inserted and a

35 proper level of contact resistance is present. Contacts A,
B and C, D are respectively spaced apart within biosensing
meter 50 and enable a determination to be made that a
sample strip 10 has been properly inserted and that its

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electrodes reflect the proper impedance states. Once such
determinations are made, sample strip 10 may be dosed,
i.e. , a drop of analyte-containing fluid placed in 'opening
20.

As is shown in Fig. 4, when a check strip 30 is inserted
into meter 50, electrode 34 makes electrical connections
with contacts A and B, whereas electrode 32 connects to a
contact C and electrode 36 connects to contact D.

Returning to Fig. 3, an excitation voltage V e is applied
from variable source 51, via line 52, to operational
amplifier 54. The output from operational amplifier 54 is
connected via analog switch 55 to contact A. A second

15 input to amplifier 54 is connected to contact B via line 56
and analog switch 57. The second input to amplifier 54 is
also connected to analog to digital converter (A/D) 58.
The output from A/D converter 58 is applied to a
microprocessor 60 which is, in turn, provided with a

20 display 62. Switches 55 and 57 are only opened during a
time that the chemical reaction is occurring in well 20, so
as to assure a high impedance condition thereacross. At
other times, switches 55 and 57 are closed.

25 On the sense side of biosensing meter 50, a line 64
connects contact C to one input of operational amplifier
66. Another input of operational amplifier 66 is connected
via line 68 to a reference potential. A resistor 70
provides the normal feedback function for operational

30 amplifier 66. The output from operational amplifier 66 is
applied via A/D converter 72 to bus 74 where it is applied
as an input to microprocessor 60.

Contact D is connected via conductor 76 and a multiplex
35 switch 78 to A/D converter 80, whose output is,, in turn,
connected to bus 74. A supply voltage source V is
connected via resistor 82 to the input to A/D converter 80.
Switch 78 is closed when meter 50 is initially powered so

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as to enable a determination to be made of the proper
insertion of sense electrode 12 . Once that determination
is made, switch 78 is opened.

5 Prior to describing the operation of the circuit shown in
Fig. 3, reference should be made to Fig. 5 wherein certain
sensed current levels are shown. If a current is sensed
flowing between electrodes 12 and 14 that falls between 0
and i t , a determination is made that a sample strip 10 has

10 been inserted and that the sensed current falls within an
acceptable current leakage range. (Recall that a sample
strip 10 is not dosed prior to insertion, but only after
biosensing meter 50 has determined that a sample strip 10
is properly inserted and acceptable) . If a current is

15 sensed that falls between i t and i 2 , biosensing meter 10
determines that a check strip 30 has been inserted and
proceeds to perform additional instrument test operations.
If the sensed current falls between i 2 and i 3 , biosensing
meter 50 determines that a test strip 10 has been inserted,

20 but that it evidences an excessive leakage current which
requires that the strip be rejected. Finally, if the
sensed current exceeds i 3 , it is determined that a short
circuit exists and the meter is automatically shut down
until the offending strip is removed.

The operation of the circuit shown in Figs. 3 will now be
described in conjunction with the logic flow diagram of
Fig. 6. It is initially assumed that either a sample strip
10 or a check strip 30 has been inserted into meter 50.

30 The insertion of a strip is determined by either an
excitation electrode 14 shorting contacts A and Tb together
or a sense electrode 12 shorting contacts C and D together.
When contact A is shorted to contact B, an excitation
voltage V e applied to contact A via operational amplifier

35 54 appears at the input to A/D converter 58. The resulting
output from A/D converter 58 enables micro-processor 60 to
detect the insertion of strip 12. In addition, micro-
processor 60 continues to monitor that output from A/D

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converter 58 to verify the applied level of V e and that
strip 10 is not removed prematurely.

In a similar manner, when a sense electrode 12 shorts
5 contact C to contact D, the potential at contact D
(Formerly at supply voltage +V) is clamped to reference
potential 68 by the action of operational amplifier 66.

At the start of operation of the circuit of Fig. 3, it is
10 assumed that meter 50 has been powered and that switch 78
is closed. In addition, an excitation potential V e is
applied from source 51 via operational amplifier 54 to
contact A. As shown in decision box 100 in Fig., 6,
microprocessor 60 initially determines whether the current
15 sensed at contact C exceeds i r if not, it is determined
that the sensed current falls within an acceptable leakage
range for a sample strip 10.

Further tests are now run to assure that sample strip 10
20 has been properly inserted into meter 50. The first test
(decision box 102) determines whether a voltage is present
on contact B that is equal to the applied excitation
voltage V e . If so, it is considered an indication that
excitation electrode 14 is continuous and properly shorts
25 contact A and B.

As above stated, A/D converter 58 senses the potential fed
back from contact B via line 56. As the feedback from line
56 to operational amplifier 54 causes operational amplifier

30 54 to exhibit a unity gain characteristic, the voltage
sensed on contact B ought to be equal to the excitation
voltage V e from source 51. The voltage identity is
determined by microprocessor 60 with a match in potentials
indicating that the test has been passed. If the

35 potentials do not match, a fault is indicated.

Next, the system determines whether the potential present
on contact D reflects the reference potential applied via

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line 68 to operational amplifier 66. This will occur only
if contact D is shorted to contact C and is clamped by
operation of operational amplifier 66 to the reference
potential level applied via line 68. If the potential on
5 contact D is not equal to the reference potential, a fault
is indicated. Assuming that the reference potential is
sensed, the system proceeds to indicate to the user that
the test strip should be dosed and that the glucose test
should then proceed.

Referring back to decision box 100, if the sensed current
is determined to exceed i $ , the procedure moves to decision
box 106 where it is determined whether the sensed current
exceeds i 2 . If not, it is determined that the sensed

15 current falls within a range designated as a check strip
range. That current results from a flow of current to
contact C through. resistance 40 when excitation voltage V 0
is applied to contact A (see Fig. 4). As will be
understood by those skilled in the art, the value of

20 resistor 40 sets the current flow to contact C and assures
that it will fall within the check strip range between i,-

If the sensed current falls within the check strip range,
25 the procedure moves to decision box 110 where the voltage
at contact B is again tested in the same manner as
described with respect to decision box 102. This tests
that excitation electrodes 34 is properly shorting contact
B to contact A. If the sensed potential at contact B is
30 other than the excitation voltage, a fault is indicated.

If the excitation voltage V e is sensed at contact B, the
procedure moves to decision box 112, where the voltage at
contact D is tested to determine if it is equal to
35 excitation voltage V e (contact 0 is shorted to contact A
via line 38) . If for some reason, electrode 32 is shorted
to electrode 36 (see Fig. 4), then the potential at contact
D will be clamped by operational amplifier 66 to the

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reference potential applied to its noninverting input. If ,
however, contact D is not shorted to contact C, the input
to A/D converter 80 will be the excitation voltage value
V e . Thus, so long as A/D converter 80 senses V e at its
5 input, that value causes microprocessor 60 to determine
that a check strip 30 is present in meter 50.

Once the presence of a check strip is confirmed, the
procedure causes an application of a plurality of

10 excitation voltage levels to operational amplifier 54.
Each applied excitation voltage level causes a different
current level to be sensed by operational amplifier 66
whose output, is in turn, converted to an appropriate
digital level by A/D converter 72. Microprocessor 60

15 responds to each output from A/D converter 72 by
determining if the outputs are within predetermined limits
and thus indicates proper operation of meter 50. If
appropriate digital values are determined (within limits),
meter 50 is indicated as being operational. If the sensed

20 current levels vary from the acceptable limits, a lockout
indication is displayed to the user which indicates that a
meter malfunction has occurred (box 116).

Returning briefly to decision box 106, if the sensed
25 current is found to exceed i 2 then, as shown in decision
box 108, it is further determined whether the sensed
current exceed i 3 . If yes, a shorted strip indication is
given. If no, a leaky strip indication is given.

30 It should be understood that the foregoing description is
only illustrative of the invention. Various alternatives
and modifications can be devised by those skilled in the
art without departing from the invention. For instance,
A/D converters 58, 72 and 80 could be replaced by a sample

35 A/D converter and fed by a multiplexer. Accordingly, the
present , invention is intended to embrace all such
alternatives, modifications and variances which fall within
the scope of the appended claims.

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11
CLAIMS

What is claimed is:

1, A biosensing meter for receiving a sample
strip that includes electrically isolated excitation and
sense electrodes that are bridged by an analyte reactant^
said biosensing meter comprising:

first and second contacts positioned to be
electrically connected by a said sense
electrode when a sample strip is inserted into
said biosensing meter;

operational amplifier means having one input
connected to said first contact and a second
input connected to a reference potential, said
one input manifesting said reference potential;
and

processor means coupled to said second contact
for determining a presence of said reference
potential at said second contact as an
indication that a sense electrode connects said
first and second contacts.

2. The biosensing meter as recited in claim l f
said processor means further comprising:

means for applying a voltage to said second
contact/ said processor means sensing said
voltage until a said sense electrode connects
said first and second contacts, at which time
said second contact- manifests said reference
potential.

3. The biosensing meter as recited in Claim 2
further comprising:

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third and fourth contacts positioned to be
electrically connected by a said excitation
electrode when a sample strip is inserted into
said biosensing meter; and

means for determining, upon an insertion of a
sample strip, that said third and fourth
contacts are electrically connected.

4. The biosensing meter as recited in claim 3,
further comprising:

means coupling said operational amplifier means
to said processor means; and

excitation supply means coupled to said third
contact, for applying an excitation voltage
thereto, whereby said processor means responds
to an output from said operational amplifier
that is at or below a first threshold level in
response to an application of an excitation
voltage to an excitation electrode, and
determines that a test strip is present that
exhibits a requisite level of electrical
isolation between its excitation and sense
electrodes.

5. The biosensing meter as recited in Claim 4,
wherein when said operational amplifier provides an output
in excess of a- second threshold level , said processor
determines that a test strip exhibits either too high a
level of leakage current or an electrical short condition.

6. A biosensing meter for receiving a sample
strip or a check strip, a sample strip including
electrically isolated excitation and sense electrodes that
are bridged by an analyte reactant, said biosensing meter
including first and second contacts positioned to be

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electrically connected by a said sense electrode when a
sample strip is inserted into said biosensing meter, a
check strip including an excitation electrode and a
segmented sense electrode, a first sense electrode segment
aligned with said first contact .- and a second sense
electrode segment aligned with said second contact, both
said sense electrode segments making respective electrical
connections with said first and second contacts upon
insertion of a check strip into said biosensing meter, said
first sense electrode segment also connected via a
resistance to a said check strip's excitation electrode,
said biosensing meter further comprising:

operational amplifier means having one input
connected to said first contact and a second
input connected to a reference potential, said
one input manifesting said reference potential;
and

processor means coupled to said second contact
for determining the presence of said reference
potential at said second contact as an

indication that a sample strip is present and
has a sense electrode that electrically connects
said first and second contacts .

7. The biosensing meter as recited in Claim 6
further comprising:

means coupling an output of said operational
amplifier means to said processor means; and

excitation means for applying an excitation
voltage to^ an inserted excitation electrode,
said processor means responsive to an output
from said operational amplifier means that
exceeds a first threshold when an excitation
voltage is applied to said excitation electrode,

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to determine that a check strip is present in
said biosensing meter.

8» The biosensing meter as recited in claim 7
wherein said resistance connecting said first sense
electrode segment to said excitation electrode is
instrumental in assuring that a said check strip causes
said operational amplifier output to exceed said first
threshold.

9. The biosensing meter as recited in claim 8 #
wherein upon determining a presence of an inserted check
strip, said processor means causes excitation means to
apply a plurality of excitation voltages to said excitation
electrode for testing operations of said biosensing meter.

10. A biosensing meter for receiving a sample strip
that includes electrically isolated excitation and sense
electrodes that are bridged by an analyte reactant, said
biosensing meter comprising:

first and second contacts positioned to be
electrically connected by a said excitation
electrode when a sample strip is inserted into
said biosensing meter;

excitation voltage means for producing an
excitation voltage;

amplifier means having one input connected to
said excitation voltage means, a second
differential input connected to said second
contact and an output connected to said first
contact; * *

processor means coupled to said second contact
for determining a presence of an excitation
voltage at said second contact as an indication

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that a said sample strip has been inserted.

11. The biosensing meter as recited in claim 10
further comprising:

switch means connected between said first
contact and said amplifier output and between
said second contact and said second input, said
switch means closed at all times except when a
chemical incubation reaction is occurring with
said analyte reactant, at which time said switch
means is open.

12. The biosensing meter as recited in claim 10
wherein said processor means continues to monitor the
presence of an excitation voltage at said second contact as
an assurance of a continued presence of a said sample
strip r until a test is completed, and of application of a
proper level of excitation voltage during a said test.

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AMENDED CLAIMS

[received by the International Bureau on 08 November 1994 (08.11.94);
original claims 1-8 and 10 amended; remaining claims unchanged (5 pages)]

1. A biosensing meter for receiving a sample strip
that includes electrically isolated excitation and sense
electrodes that are bridged by an analyte reactant, said
biosensing meter comprising:

a first contact and a second contact positioned
to be electrically connected by a sense
electrode when a sample strip is inserted into
said biosensing meter;

operational amplifier means having one input
connected to said first contact , a second input
connected to a reference potential, an output,
and a resistor directly connecting said output
to said one input, whereby said one input is
enabled to manifest said reference potential;
and

processor means coupled to said second contact
and responsive to a presence of said reference
potential at said second contact as an
indication that a sense electrode connects said
first and second contacts.

2. The biosensing meter as recited in Claim 1, said
processor means further comprising:

means for applying a voltage to said second
contact, said processor means sensing said
voltage until a sense electrode connects said
first and second contacts, at which time said
operational amplifier means enables said second
contact to manifest said reference potential.

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3. The biosensing meter as recited in Claim 2
further comprising:

third and fourth contacts positioned to be
electrically connected by an excitation
electrode when a sample strip is inserted into
said biosensing meter; and

means for determining, upon an insertion of a
sample strip, that said third and fourth
contacts are electrically connected.

4. The biosensing meter as recited in Claim 3,
further comprising:

means coupling said output of said operational
amplifier means to said processor means; and

excitation supply means coupled to said third
contact for applying an exditation voltage
thereto, said processor means responding to an
output from said operational amplifier that is
at or below a first threshold level when said
excitation voltage is applied to said third
contact and to a connected excitation electrode,
by determining that a sample strip exhibits a
requisite level of electrical isolation between
its excitation and sense electrodes.

5. The biosensing meter as recited in Claim 4,
wherein if said operational amplifier provides an output in
excess of a second threshold level, said processor
determines that said sample strip exhibits either too high
a level of leakage current or an electrical short
condition.

6. The biosensing meter for receiving a sample strip
or a check strip, a sample! strip including electrically

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isolated excitation and sense electrodes that are bridged
by an analyte reactant, said biosensing meter including
first and second contacts positioned to be electrically
connected by a sense electrode when a sample strip is
inserted into said biosensing meter, a check strip
including an excitation electrode and a segmented sense
electrode, a first sense electrode segment aligned with
said first contact and a second sense electrode segment
aligned with said second contact, both said sense electrode
segments making respective electrical connections with said
first and second contacts upon insertion of a check strip
into said biosensing meter, said first sense electrode
segment also connected via a first resistance to a said
check strips excitation electrode, said biosensing meter
further comprising:

operational amplifier means having one input
connected to said first contact, a second input
connected to a reference potential, and an
output directly connected by a second resistance
to said one input to create a feedback path,
whereby said one input manifests said reference
potential ; and

processor means coupled to said second contact
and responsive to a presence of said reference
potential at said second contact as an
indication that a sample strip is present and
has a sense electrode that electrically connects
said first and second contacts.

7. The biosensing meter as recited in Claim 6
further comprising:

means coupling said output of said operational
amplifier means to said processor means; and

excitation means for applying an excitation

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PCT/US94/05322

voltage to an inserted excitation electrode of a
check strip, and for causing, via said first
resistance, a voltage to appear at said sense
electrode which exceeds a first threshold, said
processor means responsive to an output from
said operational amplifier means that a voltage
is present on said sense electrode that exceeds
said first threshold to determine that a check
strip is present in said biosensing meter.

8. The biosensing meter as recited in Claim 7
wherein said first resistance connecting said first sense
electrode segment to said excitation electrode is
instrumental in assuring that a said check strip causes
said operational amplifier output to exceed said first
threshold.

9. The biosensing meter as recited in Claim 8,
wherein upon determining a presence of an inserted check
strip, said processor means causes excitation means to
apply a plurality of excitation voltages to said excitation
electrode for testing operations of said biosensing meter.

10. A biosensing meter for receiving a sample strip
that includes electrically isolated excitation and sense
electrodes that are bridged by an analyte reactant, said
biosensing meter comprising:

first and second contacts positioned to be
electrically connected by an excitation
electrode when a sample strip is inserted into
said biosensing meter;

excitation voltage means for producing an
excitation voltage;

amplifier means having one input connected to
said excitation voltage means a second

PCT/US94/05322

differential input connected to said second
contact and an output connected to said first
contact;

processor means coupled to said second contact
for determining a presence of an excitation
voltage at said second contact as an indication
that a sample strip has been inserted and for
monitoring said excitation voltage at said
second contact at least when said switch means
are closed, as an assurance of a continued
presence of a said sample strip, until a test is
completed, and of application of a proper level
of excitation voltage during a test .

WO 94/29705

PCT/US94/05322

WO 94/29705

PCT/US94/05322

FIG. 4.

2/3

•r

30-
t-

32'

38~!
40

~36

FIG. 5.

SENSE

t 3 +
0

^SHORTED STRIP
J RANGE

LEAKY STRIP
J RANGE

„ CHECK STRIP
J RANGE

}

ACCEPTABLE
LEAKAGE

SUBSTITUTE SREIf (Rflli 26)

WO 94/29705

PCT/US94/05322

3/3

FIG. 6.

114

APPLY LEVELS OF
V e TO CONTACT A

a DETERMINE
SENSE CURRENT
OUTPUTS

116

IF SENSE CURRENT
OUTPUT «>/, N RANGE
SIGNAL OKj I F NOT
-SIGNAL FAULT

SUBSTITUTE SHEET (RULE 26)

INTERNATIONAL SEARCH REPORT

International application No.
PCT/US94/05322

A. CLASSIFICATION OF SUBJECT MATTER

IPC(5) :G01N 27/26
US CL :324/438, 525; 422/82.02; 204/401
According to International Patent Classification (IPC) or to both national classification and IPC

B. FIELDS SEARCHED

Minimum documentation searched (classification system followed by classification symbols)
U.S. : 324/438, 439, 446, 450, 525, 538, 603, 692, 693; 422/82.02; 204/401 , 406

Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched

Electronic data base consulted during the international search (name of data base and, where practicable, search terms used)

C. DOCUMENTS CONSIDERED TO BE RELEVANT

Category*

Citation of document, with indication, where appropriate, of the relevant passages

Relevant to claim No.

US, A, 4,999,582 (PARKS et al), 12 MARCH 1991, figure 3
and column 3, lines 42-54.

US, A, 3,996,514 (BROWN et al) 07 DECEMBER 1976, see
the abstract and figures 1-4.

US, A, 5,266,179 (NAIMKAI et al) 30 NOVEMBER 1993, see
the abstract and figures 4-9.

US, A, 5,053,199 (KEISER et al) 01 OCTOBER 1991, see
the entire document.

US, A, 4,714,874 (MORRIS et al) 22 DECEMBER 1987, see
the entire document.

10, 11

Y
Y

Y,P

A
A

1-9, 12
1-9, 12

4. 5, 7-9

1-12
1-12

fx) Further documents are listed in the continuation of Box C. [""] Sec patent family annex.

• Specal caicforK* of cit«J documents: T bier document pubtbfaed liter the blcnimtmittJ filinf dMc or priority

•A' docur^defu^sthe^^c^tbe^whkh b «* cohered SSb««E?^

to be c*n of pwticubx relevance principle or theory underrymf the mveoboo

*E* earlier document published on or after the internatiofftaj filine date document of particular relevance; the churned invention cannot be

cooaidered novd or cannot be conaidcred to involve an inventive ttep
L document which may throw doubto on priority cbimft) or which b when the document b taken alone
cited to establish the publication dale of another citation or other

special reason (a* specified) * Y* document of particular relevance; the churned invention cannot be

•r>» -» . .... . , . . considered to involve an inventive step when the document b

J"*™** t**™** U> an oral daciosure. use. exhibition or other combined with one or more other such dc^m^. such «^instion
means bcinf obvious to • person skilled in the art

Date of the actual completion of the international search
12 JULY 1994

Date of mailing of the international search report

21 SEP 1394

Name and mailing address of the ISA/US
Commissioner of PitenU sod Trademarks

Box per

Washington, D.C. 20231
Facsimile No. (703) 305-3230

^SNNETHWIEDER
Telephone No. (703) 305-4900

Form PCT/1SA/210 (second sheetXiuly 1992)*

INTERNATIONAL SEARCH REPORT

International application No.
PCT/US94/Q5322

C (Continuation). DOCUMENTS CONSIDERED TO BE RELEVANT

Category*

Citation of document, with indication, where appropriate, of the relevant passages

Relevant to claim No.

US, A, 4,680,537 (MILLER) 14 JULY 1987, see the entire
document.

1-12 i

Form PCT/1SA/210 (continuation of second sheet)(Juiy 1992)*

THIS PAGE BLANK (uspto)

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